1. Field of the Invention
The present invention relates to polyamide/polyurethane composite filament yarns having a crimpability, a process and a spinneret for manufacturing the same and hosiery, such as stockings or the like, knitted therewith.
2. Related Art Statement
It is known that composite filaments consisting of polyamide and polyurethane components conjugated eccentrically with each other in a unitary filament have an excellent crimpability (Japanese Patent Application Publication Nos. Sho-55-22,570 and 55-27,175). However, side-by-side type composite filaments, for example, such as shown in FIG. 4, though excellent in crimpability, have a drawback such that separation of the components and deterioration of physical properties are caused by bending or abrasion during processing steps or wearing of textile articles composed of such filaments, due to insufficient compatibility of both components. Another drawback is polyurethane components exposed on the surface of the filament stick to each other due to retarded solidification of polyurethane melt, so that as-spun and wound filament yarns cannot be unwound from a yarn package due to sticking.
Alternatively, whereas sheath and kidney-like core type composite filaments as shown in FIG. 5 which have been proposed, for example, in Japanese Patent Application Publication No. Sho-55-27,175, have solved the problems presented by the side-by-side type composite filaments, such filaments still have a drawback that crimp developability, by virtue of difference in shrinkage between a high shrinking polyurethane component and a low shrinking polyamide component, is poor because the polyurethane core component is completely surrounded with the polyamide sheath component.
Further, even with the combination of a polyamide component with a polycarbonate based polyurethane component, which has relatively good compatibility, the adhesiveness between these components are still insufficient, so that there occurs a phenomenon such that two components split during the yarn manufacturing process or the wearing of stockings, or the like. For example, in sheath and kidney-like core type composite filaments as shown in FIG. 5, external stresses, such as elongation, bending, abrasion, heat treatment, or the like, concentrate on thin edge portions, C.sub.1.about.C.sub.2 and C.sub.1 '.about.C.sub.2 ', where the sheath eventually breaks and the two components separate from each other along the line C.sub.1.about.C.sub.1 '.
Therefore, in order to solve the problems of poor adhesiveness of two components, inferior abrasion resistance of articles and sticking of polyurethane components to each other, which include polyamide/polyurethane side-by-side type composite filament yarns, we, the inventors, have proposed in Japanese Patent Application Laid-open No. Sho-63-256,719, as composite filaments having an excellent crimpability, as compared with the above-mentioned sheath and kidney core type composite filaments, composite filaments as shown in FIG. 6 wherein a large part of a polyurethane component is surrounded with a polyamide component and a small part of the polyurethane component is exposed on the surface of the filament, and a process for spinning such composite filaments with a spinneret as shown in FIG. 2. Namely, the spinneret shown in FIG. 2 comprises a vertical conduit 2 extending from a polyamide leading duct 1, having an orifice 3 of small diameter opening downwards, and an injection pipe 5 extending obliquely downwards from a polyurethane leading duct 4, having a tip end portion protruding into said conduit 2. The degree of protrusion is adjusted to an extent that the inner circumference of the opening tip end of the injection pipe 5 is just tangent internally to the inner circumference of the conduit 2. With such a spinneret, incomplete sheath and core type composite filaments as shown in FIG. 5 are obtained, wherein a polyurethane component, B tangent internally to a polyamide component A, is barely exposed at the contact point on the surface of the filament.
In the cross-sectional shape of such a filament, the polyamide component A surrounds most of the polyurethane component and gradually decreases its thickness along its periphery, so that stress concentration as aforementioned is relaxed and excellent adhesion is obtained between the polyamide and polyurethane components. This stops both components from splitting easily and sticking of polyurethane components to each other can be prevented between asspun filament yarns wound on a take-up roll.
However, whereas the above-mentioned composite filaments proposed by the present inventors, provided with excellent physical properties, have succeeded in obviating all of the aforementioned prior art difficulties, these filaments have been found to have another drawback such that when the spinning is conducted with the above-mentioned spinneret, the cross-sectional shape of the filament, particularly the width d in FIG. 6 of the exposed polyurethane component, largely varies due to the fluctuation of melt viscosity caused by a slight temperature variation.
Further, both the side-by-side type and sheath and kidney-like core type filaments have a problem of fisheyes caused by a poor stability of the polyurethane melt during spinning.
By fisheye is meant a local thick portion in drawn filament after spinning, winding and drawing, which causes poor draw-twisting operability of undrawn filament yarns as well as inferior qualities of articles, such as stockings, composed of the filament yarns.
Throughout this specification, the number of fisheyes is a value obtained by counting thick portions having a diameter five times the normal diameter of the unitary filament constituting a drawn yarn and converting the count to the number per 1 kg of a filament yarn.